The invention relates to a method for laminating photovoltaic modules and similar, essentially plate-shaped work pieces, which include at least one thermally activated adhesive layer under the influence of pressure and heat.
In such a method, usually a one-layer or multi-layer vacuum lamination press is used comprising one, and in the multi-layer case several, vacuum chambers. The vacuum chamber is formed by an upper and a lower chamber half, which are movable in reference to each other in order to open and close the vacuum chamber. It is divided in a gas-tight fashion by a compression means, and said compression means can be raised or lowered within the vacuum chamber by way of pressure differences.
Commonly such compression means represent a flexible diaphragm, which divides the vacuum chamber into a product chamber that can be evacuated and is embodied to accept at least one work piece, and a pressure chamber that can be evacuated and/or impinged with pressure. Due to a pressure difference generated in the vacuum chamber by evacuating the product chamber and/or by impinging the pressure chamber with pressure, the flexible diaphragm is pressed against the work piece, thus pressing the work piece directly or indirectly against a plate limiting the vacuum chamber, in the normal case the floor of the vacuum chamber, with perhaps a conveyer belt traveling between the plate and the work piece, and the load required for lamination being applied thereby onto the work piece. In general, this plate, usually the bottom of the vacuum chamber, is formed by a heating plate so that the processing heat necessary for lamination is directly introduced into the work piece.
In a method according to the present type, particularly a photovoltaic module or several work pieces, simultaneously is/are introduced into the vacuum chamber of the vacuum lamination press used, and the vacuum chamber is closed; for reasons of simplification, in the following only one work piece is being discussed. Then the vacuum chamber is evacuated and the compression means is pressed against the work piece by way of ventilating and/or impinging with pressure the part of the vacuum chamber not housing any work piece and said piece is thereby directly or indirectly pressed against the plate limiting the vacuum chamber. This plate is usually the bottom of the vacuum chamber.
The process heat required for the lamination process is usually transferred into the work piece by the bottom of the vacuum chamber which is embodied as a heating plate, with the work piece being pressed against it by the compression means. The pressure and the process heat combined then ensure the softening and/or activation of the adhesive layer and, if applicable, also its curing and/or cross-linking. However, other forms of inserting process heat are also possible.
Usually the evacuation of the vacuum chamber occurs such that first the pressure chamber of the vacuum chamber located above the compression means is evacuated in order to pull the compression means upwards towards the upper chamber half. Then, usually temporarily off-set, the product chamber comprising the work piece and located underneath the compression means is evacuated, with the evacuation of both chambers of the vacuum chamber being controlled such that always a pressure difference remains between the pressure chamber and the product chamber, which keeps the compression means in the upper half of the chamber and prevents that the compression means prematurely contact the work piece.
When the product chamber of the vacuum chamber has been evacuated to a target pressure, which usually is below one millibar, the pressure chamber is ventilated so that the pressure difference inverses between the pressure chamber and the product chamber, and the compression means contacts the work piece. Then a desired compression of the compression means is adjusted, usually by controlling the gas pressure in the pressure chamber, in order to generate the required load on the work piece necessary for lamination.
Here, according to prior art, particularly the product chamber of the vacuum chamber shall be evacuated rapidly, namely prior to any relevant heating of the work piece, at least prior to the activation of the adhesive effect of the adhesive layer. This allows that potential air enclosures (air trapped between the layers of the work piece) or gases potentially developing during the heating process are evacuated from the work piece before any curing and/or cross-linking of the adhesive in the adhesive layer begins. Because gas bubbles in the finished laminated work piece considerably compromise its life span or, in the worst case scenario, lead to an immediate worthlessness of the work piece, thus the production of discards. This particularly applies to photovoltaic modules.
WO 94/29106 A1 describes a method for laminating photovoltaic modules with adhesive layers that can be cured under the influence of pressure and heat. Here, a vacuum lamination press is used, in which a diaphragm is arranged as a flexible compression means, which divides the vacuum chamber into a product half and a pressure half. The process heat is inserted via a heating plate into the photovoltaic module, which indirectly impinges the work piece through a support plate. Upon closing the vacuum chamber it is rapidly evacuated in order to remove trapped air and other gases from the photovoltaic module before it is considerably heated. Then the compression half of the vacuum chamber located above the diaphragm is ventilated so that the diaphragm applies a load upon the work piece, generated by the pressure difference, and particularly also starts and/or accelerates the heat transfer from the heating plate into the work piece.
In WO 94/29106 A1 the photovoltaic modules in the vacuum lamination press are only preliminarily laminated because the vacuum chamber is opened without any cooling process, the preliminarily laminated work pieces are transferred into a curing kiln, and here the adhesive layers are hardened at high temperatures. Here, it is utilized that the adhesive layers commonly used in photovoltaic modules develop such an adhesive effect already at the beginning of the curing and/or cross-linking process so that any penetration of air from the outside of the work piece between its individual layers no longer needs to be feared at an early period of time and the further lamination therefore no longer needs to occur in a vacuum. When the work pieces no longer need to remain in the vacuum lamination press until the adhesive layers are entirely cured and/or cross-linked, but the further curing and/or cross-linking can occur in the curing kiln, the clock time of the vacuum lamination press and thus the processing speed of the entire installation can be increased.